A study of the molecular structure and vibrational spectra of 1,3-dichloro-2-propanol and 1,1,1-trichloro-2-methyl-2-propanol (chlorobutanol)

The conformational stability of 1,3-dichloro-2-propanol and 1,1,1-trichloro-2-methyl-2-propanol (chlorobutanol) was investigated by the DFT-B3LYP/6-311+G**, MP2/6-311+G** and MP4(SDQ)/6-311+G** levels of theory. From the calculations chlorobutanol was predicted to exist in a non-planar gauche structure. The planar cis and trans structures of chlorobutanol were calculated to be about 3 kcal/mol higher in energy than the gauche structure. From the calculations 1,3-dichloro-2-propanol was predicted to exist in a Ggg1 and Ggg conformational mixture at ambient temperature. In the low energy structures of both alcohols the non-bonded Cl⋯H(O) distance was calculated to be of about 2.6-2.7 . The observation of a broad and very intense band at about 3400 cm ^-1 in the infrared spectra of the two alcohols supports the presence of strong intermolecular Cl⋯H(O) dipolar interactions in their condensed phases. The analysis of the Raman spectra of 1,3-dichloro-2-propanol suggests the presence of a second high energy Ggg structure of the dichloride at room temperature. The vibrational frequencies of 1,3-dichloro-2-propanol and chlorobutanol in their low energy structures were computed at the B3LYP level and tentative vibrational assignments were made for their normal modes on the basis of combined calculated and experimental data.